Vapor compression refrigeration cycle to perform cooling and heating of fluids by the use of state change of material such as evaporation and condensation has found a widespread use for applications such as an air-conditioner, refrigerator, hot-water supplier, etc. A variety of working fluids which are applied for the vapor compression refrigeration cycle, especially fluorocarbon refrigerants, have been developed and practically used. Among the fluids, HCFC22 (monochlorodifluoromethane) is widely used as a refrigerant in a heating and cooling system for air-conditioning.
However, chlorofluorocarbons were recently found to be responsible for the destruction of the ozone layer when released into the stratosphere and eventually exert seriously adverse effects on the ecosystem including human on the earth. Then, a worldwide agreement calls for the restriction of use and in the future total abolition thereof. Under these circumstances, there is an urgent demand for developing a new refrigerant which has no or little potential to cause the problem of depleting the ozone layer.
As attempts to make up for insufficient performances of a single component refrigerant by the use of refrigerant blends, many proposals for using non-azeotropic refrigerant blends have recently been raised (e.g., Japanese Unexamined Patent Publication No. 79288/1989, Japanese Examined Patent Publication No. 55942/1994, and Japanese Unexamined Patent Publication No. 287688/1991).
A non-azeotropic mixture causes a composition change during phase change such as evaporation and condensation, since a component having lower boiling point is likely to be evaporated and a component having higher boiling point is likely to be condensed. The tendency of composition change is pronounced in the case of evaporation, i.e., phase change from liquid to vapor, and the tendency is particularly pronounced as differences of boiling point between components are larger. Therefore, when such a non-azeotropic blend is transferred from one container to another, it is common practice to discharge it from liquid phase so as not to arise the phase change. However, even in the case of discharging a refrigerant blend from liquid phase, phase change as much as a few percent occurs in the case where the differences in boiling points are large between components. This is because discharging the blend causes a decrease of pressure and increase of the gaseous space, resulting in evaporation of lower-boiling-point components from liquid phase. A few percent of composition change cause a significant change in performances of refrigerant, and the change not only results in a decrease in capability and efficiency of the refrigerant, but also adversely affects safety of refrigerants such as flammability.
In particular, when using as a refrigerant a non-azeotropic blend comprising 23% by weight of difluoromethane (thereafter referred to as "HFC32"), 25% by weight of pentafluoroethane (thereafter referred to as "HFC125") and 52% by weight of 1,1,1,2-tetrafluoroethane (thereafter referred to as "HFC134a"), which is considered as the most promising substitute for HCFC22, the composition change thereof caused during transfer of the refrigerant from a bomb and like feeding container, to an air-conditioner is a serious problem, since ASHRAE STANDARD (1994) establishes the permissible composition range of HFC32(21-25% by weight), HFC125(23-27% by weight) and HFC134a(50-54% by weight).
As a method to solve the problem, Japanese Unexamined Patent Publication No. 157810/1996 proposes a method for allowing the composition to fall within the range of the tolerance of the composition by increasing in the blend composition lower boiling point components beforehand which are decreased with composition change.
Since a permissible range of performance of refrigerant is usually within .+-.3% by weight, in particular .+-.2% by weight with respect to the standard value, a biased composition concerning lower-boiling-point components according to the method enlarges differences of performance of refrigerant from the standard value.